The effect of portacaval shunt on hepatic lipoprotein metabolism in familial hypercholesterolemia

Lomitapide and Mipomersen-Inhibiting Microsomal Triglyceride Transfer Protein (MTP) and apoB100 Synthesis

PURPOSE OF REVIEW

The goal of this review is to evaluate the role of inhibiting the synthesis of lipoproteins when there is no or little residual LDL-receptor function as in patients with homozygous familial hypercholesterolaemia. Lomitapide is administered orally once a day while mipomersen is given by subcutaneous injection once a week. Lomitapide inhibits microsomal triglyceride transfer protein while mipomersen is an antisense oligonucleotide directed against apoB100.

RECENT FINDINGS

The pivotal registration trials for lomitapide and mipomersen were published in 2013 and 2010, respectively. More recently published data from extension trials and cohort studies provides additional information on long-term safety and efficacy. The mean LDL cholesterol reduction was 50% with lomitapide in its single-arm open-label registration trial. Mipomersen reduced LDL cholesterol by approximately 25% in its double-blind, placebo-controlled registration study. Both lomitapide and mipomersen therapy are associated with variable increases in hepatic fat content. The long-term safety of increased hepatic fat content in patients receiving these therapies is uncertain and requires further study. Both drugs may cause elevated transaminase in some patients, but no cases of severe liver injury have been reported. Lomitapide may also cause gastrointestinal discomfort and diarrhoea, especially if patients consume high-fat meals and patients are advised to follow a low-fat diet supplemented with essential fatty acids and fat-soluble vitamins. Mipomersen may cause injection-site and influenza-like reactions. The effect of lomitapide and mipomersen on cardiovascular outcomes has not been studied, but circumstantial evidence suggests that the LDL cholesterol lowering achieved with these two agents may reduce cardiovascular event rates.

Low total, low-density lipoprotein, high-density lipoprotein, and non-high-density lipoprotein cholesterol levels in patients with complex congenital heart disease after Fontan palliation

OBJECTIVE

To test the hypothesis that patients with complex congenital heart disease who have undergone Fontan palliation have low total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) levels.

STUDY DESIGN

We retrospectively reviewed the random serum lipid profiles obtained at cardiology clinic visits between May 2010 and November 2011 in patients who had undergone the Fontan procedure. We compared these serum lipid levels against age- and sex-matched established normal data from the Third National Health and Nutrition Examination Survey.

RESULTS

Eighty-eight patients who had undergone the Fontan procedure also had laboratory test data obtained during their visits. Median total cholesterol level in the Fontan group was 127 mg/dL (IQR, 116-144 mg/dL), median HDL-C was 40 mg/dL (IQR, 33-45 mg/dL), median non-HDL-C was 86 mg/dL (IQR, 76-109 mg/dL), and median LDL-C was 66 mg/dL (IQR, 57-83 mg/dL). Total cholesterol, LDL-C, non-HDL-C, and HDL-C levels were significantly lower in patients who had undergone a Fontan procedure compared with age- and sex-matched normal individuals (mean z-score, -1.4, -1.2, -1.0, and -1.0 respectively; all P<.0001). Cholesterol levels were below the 25th percentile for age and sex for total cholesterol in 82% of patients, for LDL-C in 76%, for non-HDL-C in 67%, and for HDL-C in 57%.

CONCLUSION

Patients who have undergone the Fontan procedure have significantly lower serum total cholesterol, LDL-C, HDL-C and non-HDL-C levels than age- and sex-matched normal individuals. Although the implications of this finding are unknown, it raises the possibility of abnormalities in cholesterol absorption, synthesis, or catabolism in this patient population.

Non-pharmacological lowering of low-density lipoprotein by apheresis and surgical techniques

In the past year, new data have appeared on the long-term benefits of low-density lipoprotein apheresis in severely hypercholesterolemic patients who are refractory to lipid-lowering drug therapy. Such data are critical for clinical decision-making, because they confirm the hypothesis that the dramatic reduction in low-density lipoprotein made possible by this technique produces clear-cut clinical benefits. Because of its efficacy and low incidence of side-effects, apheresis for severe drug-refractory hypercholesterolemia has superseded surgical approaches, such as liver transplantation or ileal bypass.

Detection and quantitation of calcific atherosclerosis by ultrafast computed tomography in children and young adults with homozygous familial hypercholesterolemia

Ultrafast computed tomography (CT) is a new method for detecting calcific lesions in the coronary arteries. The ability of CT to detect and quantify coronary artery atherosclerosis in children and young adults at risk for malignant atherogenesis was evaluated. A total of 11 consecutive familial hypercholesterolemic (FH) homozygotes (3 to 37 years old) participated. Untreated total cholesterol concentrations were 488 to 1277 mg/dL (12.7 to 33.2 mmol/L). Angiography detected significant lesions in 7 of 11 patients. CT detected calcific atherosclerosis in all 9 of the patients older than 12 years of age, including all those with angina. CT was more sensitive in detecting aortic root and coronary ostial lesions, where atherosclerosis first appears in homozygous FH. The volume of calcification (in cubic millimeters) correlated with the severity and duration of the hypercholesterolemia (r = .62, P < .05) as well as with the presence of angina (P < .05). All patients with angina (7 of 7) had > 150 mm3 of calcified volume, whereas only 1 of 4 asymptomatic patients had a volume score > 150 mm3. We conclude that (1) coronary and aortic calcium phosphate deposits are common in young FH homozygotes; (2) these deposits are associated with the presence of angiographic stenoses, as has been seen in adults with coronary atherosclerosis; and (3) aortic calcific deposits are more common than calcific coronary lesions.

Pharmacologic and surgical treatment of dyslipidemic children and adolescents

A wide variety of treatment modalities have been used in children with dyslipidemias to reduce the concentrations of atherogenic lipoprotein particles. Most of the published experience has focused upon children with familial hypercholesterolemia (FH). A variety of pharmacologic regimens have been utilized with variable degrees of success. The bile acid sequestrants colestipol and cholestyramine, lovastatin, pantethine, paraminosalicylic acid, and fenofibrate have all been successful in reducing total blood cholesterol concentrations by 18-24% in hypercholesterolemic children. Of these medications, only the bile acid sequestrants are not absorbed into the circulation. This theoretic advantage is paralled by long-term safety studies which indicate the absence of serious adverse effects with bile acid sequestrant therapy. Therefore, the bile acid sequestrants represent the drugs of choice in treating severely dyslipidemic children. In selected cases of profoundly dyslipidemic children, other therapeutic strategies have been utilized. Most of these efforts have been directed in the treatment of the child homozygous for FH. Despite the lipid lowering effects of partial ileal bypass surgery in hypercholesterolemic adults, homozygous familial hypercholesterolemic children are not adequately treated by this approach. Portacaval shunt has reduced the total cholesterol concentrations by 20-35% in homozygous FH children without having a negative impact on growth and development. These children have, however, gone on to develop atherosclerotic cardiovascular disease despite therapy. Liver transplantation has led to virtual normalization of the plasma lipoprotein concentrations in 3 children homozygous for familial hypercholesterolemia, and there is evidence for regression of vascular lesions in the coronary arteries in one of these children. However, considering the expense, the difficulty in posttransplantation management, and the irreversible nature of the therapy, liver transplantation should be reserved as the therapy of last resort for homozygous FH. The best therapy for FH homozygotes is the frequent removal of the atherogenic lipoproteins by one of the several apheresis procedures currently available. Total plasma exchange, immunoadsorption, membrane filtration, dextran sulfate adsorption, and heparin extracorporeal precipitation have all been used successfully in significantly reducing the concentrations of total and low-density lipoprotein cholesterol. Studies currently under way will more extensively evaluate the long-term safety as well as the efficacy of apheresis procedures.